Engine coolants for the cooling system of automotive vehicles usually contain ethylene glycol with a small percentage of diethylene glycol diluted with water to provide a 50% or lower concentration of glycol depending on the desired freezing point for the coolant system. Most companies that manufacture and/or distribute ethylene glycol for coolant systems add corrosion inhibitors to the solution to prevent corrosion of the copper-brass material traditionally used in the manufacture of vehicle radiators.
These inhibitors usually are a mixture of one or more inorganic salts, such as phosphates, borates, nitrates, nitrites, silicates and/or arsenates, along with an organic compound, such as benzotriazole, tolyltriazole or mercaptobenzothiazole, to prevent copper corrosion. The solution is generally buffered to a pH in the range of 8-10 to reduce iron corrosion and to neutralize any glycolic acid formed in the oxidation of ethylene glycol. Most companies recommend only one or two years' service for their antifreeze coolant, however, the average car owner does not follow the owner's instruction manual to maintain -20.degree. F. protection for the coolant system and does not periodically check the coolant to determine if it is rusty or dirty. Vehicle owners will normally only add water where the antifreeze coolant is lost through leakage, hose breakage or overheating due to mechanical problems.
In normal passenger car service, 25% of the cars require coolant system servicing after one year and, after two years, this percentage rises to 50%. With a copper-brass radiator, it is extremely important that the coolant mixture contain 50-55% of the properly inhibited ethylene glycol. A reduction of 33% ethylene glycol and 67% water with a corresponding reduction in the inhibitor level will increase metal corrosion significantly. This is especially important in high temperature coolant systems which are becoming more common in view of the increased use of emission controls. Also, the corrosion inhibitor may lose its effectiveness with age and its use in a coolant system will result in an increase in corrosion of the metallic parts of the coolant system.
With the increasing emphasis on gas mileage of automobiles, cars are being downsized and reduced in weight by the substitution of lightweight metals or plastic for the traditional materials. In the coolant system, aluminum radiators are being substituted for previously used copper-brass radiators, and aluminum is more susceptible to the corrosive action of a coolant that is low in the percentage of ethylene glycol and/or corrosion inhibitor. In such a system, additional corrosion inhibitor must be added or the aluminum will begin to corrode by pitting at a rapid rate. The present invention overcomes this corrosion problem by providing for a substantially continuous automatic additon of corrosion inhibitor to the coolant.